RESUMEN
Meta-atoms are the building blocks of metamaterials, which are employed to control both generation and propagation of light as well as provide novel functionalities of localization and directivity of electromagnetic radiation. In many cases, simple dielectric or metallic resonators are employed as meta-atoms to create different types of electromagnetic metamaterials. Here, we fabricate and study supercrystal meta-atoms composed of coupled perovskite quantum dots. We reveal that these multiscale structures exhibit specific emission properties, such as spectrum splitting and polaritonic effects. We believe that such multiscale supercrystal meta-atoms will provide novel functionalities in the design of many novel types of active metamaterials and metasurfaces.
RESUMEN
Ultrafast all-optical modulation with optically resonant nanostructures is an essential technology for high-speed signal processing on a compact optical chip. Key challenges that exist in this field are relatively low and slow modulations in the visible range as well as the use of expensive materials. Here we develop an ultrafast all-optical modulator based on MAPbBr3 perovskite metasurface supporting exciton-polariton states with exceptional points. The additional angular and spectral filtering of the modulated light transmitted through the designed metasurface allows us to achieve 2500% optical signal modulation with the shortest modulation time of 440 fs at the pump fluence of â¼40 µJ/cm2. Such a value of the modulation depth is record-high among the existing modulators in the visible range, while the main physical effect behind it is polariton condensation. Scalable and cheap metasurface fabrication via nanoimprint lithography along with the simplicity of perovskite synthesis and deposition make the developed approach promising for real-life applications.
RESUMEN
Optical data storage, information encryption, and security labeling technologies require materials that exhibit local, pronounced, and diverse modifications of their structure-dependent optical properties under external excitation. Herein, we propose and develop a novel platform relying on lead halide Ruddlesden-Popper phases that undergo a light-induced transition toward bulk perovskite and employ this phenomenon for the direct optical writing of multicolor patterns. This transition causes the weakening of quantum confinement and hence a reduction in the band gap. To extend the color gamut of photoluminescence, we use mixed-halide compositions that exhibit photoinduced halide segregation. The emission of the films can be tuned across the range of 450-600 nm. Laser irradiation provides high-resolution direct writing, whereas continuous-wave ultraviolet exposure is suitable for recording on larger scales. The luminescent images created on such films can be erased during the visualization process. This makes the proposed writing/erasing platform suitable for the manufacturing of optical data storage devices and light-erasable security labels.
RESUMEN
This study continues a series of studies by Stewart and Merbs on vertebral column variations in Eskimo groups. The focus is on so called cranio-caudal shifts in spine patterning. The study is performed on a skeletal sample of ancient Eskimos from Siberia (Ekven site, Chukotka) and comparative samples representing population groups of European and African ancestry. In addition to these, literature data are used for comparative analysis to assess the pattern of cranio-caudal border shifts on intra-specific level. The result confirms the presence of significantly increased predisposition of the Eskimos to caudal shifts in spine patterning, expressed both as increased frequencies of complete caudal shifts of thoraco-lumbar and lumbo-sacral borders, as well as minor variations in vertebrae morphology, including variation in the type of articular processes (thoracic/lumbar types) and the position of costo-central articulation at T9 level. Hypotheses explaining this specific character of the Eskimo/Inuit groups are proposed and explored, including gene drift, influence of environmental factors and association with morphological characteristics adaptive to survival in the Arctic. One of the explanations may be the association with characteristic form and size of the thoracic cage that distinguishes the Arctic groups such as Eskimos and Chukchi from groups leaving in more southern areas. This needs to be tested on other groups, living in similar conditions
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